1. Field of the Invention
This invention relates generally to rotary shears employed to subdivide hot rolled bar products in rolling mills, and is concerned in particular with the provision of an improved and simplified drive for such shears.
2. Description of the Prior Art
Rotary shears are widely employed to subdivide hot rolled bar products ranging from 16 mm rounds traveling at 18 m/s to 60 mm rounds traveling at 2 m/s.
Conventionally, the shears are driven by single ratio gear drives, typical examples of which are illustrated in FIGS. 3A-3D. In each drive arrangement, the gears are arranged symmetrically with respect to the shear center line “CL”. Thus, in the drive arrangement shown in FIG. 3A, the upper and lower blade shafts 10 carry gears 12 mechanically coupled by idler gears 14, with the lower blade shaft being directly driven by a coaxial input shaft (not shown).
FIG. 3B discloses a similar symmetrical gear arrangement, the difference being that the lower gear 12 is driven by a pinion 16 on an offset input shaft 18.
With these drive arrangements, the shears are incapable of handling the larger product sizes because the idler gears 14 are too small and weak. The drive arrangement of FIG. 3A is additionally compromised by a low moment of inertia.
In the drive arrangement shown in FIGS. 3C and 3D, the blade shafts 10′ carry large diameter intermeshed gears 20. In the drive arrangement illustrated in FIG. 3C, the bottom gear 20 is driven directly by a coaxial input shaft (not shown). If the gears 20 are thin and lightweight, the shear can cut the smaller bars, but the relative fragility of such gears will rule out shearing the larger product sizes. Conversely, if the gears 20 are heavier and more robust, the shear will be incapable of handling smaller bars due to the resulting increase in moment of inertia.
In the arrangement illustrated in FIG. 3D, where the lower gear 20 is again driven by a pinion 16 carried on an offset input shaft 18, increased inertia again precludes shearing the range of smaller bars.
Thus, the shearing of the entire range of bar sizes typically requires the use of at least two shears, one being dedicated to the subdivision of the smaller bars traveling at the higher speeds, and the other being dedicated to the larger bars traveling at the lower speeds, where greater inertia is required.
In a more recent development, as described in US2006/0278054A1, a single rotary shear has a dual ratio gear drive which may be selectively operated to provide a higher cutting speed for the smaller bar products and a lower cutting speed, augmented where necessary by a fly wheel, to provide high inertia for the larger bar products.
The conventional use of multiple shears is disadvantageous in that it increases initial capital investment and subsequent maintenance costs. Although these problems are alleviated to some extent by the use of a single shear capable of subdividing the entire range of bar products, the dual ratio gear drive employed to achieve this broader capability is itself complicated and costly.
The objective of the present invention is to provide a shear capable of handling the entire range of bar products, with a less complicated and expensive single ratio gear drive.